The present invention relates to an electronic unit operable in conjunction with a body unit, in which the body unit is fixedly mounted on an automotive vehicle and an electronic unit is detachably coupled to the body unit.
Recent audio or video equipments mounted on automotive vehicles are provided with an anti-theft function, so that such equipments illegally detached from an automobile are rendered invalid when used in another automobile. Or, to prevent an electronic equipment from being stolen, the equipment is detachably mounted on the vehicle so that the owner of the equipment can carry it out when he leaves his car. When such an electronic unit is used in his own car, the electronic unit is coupled to a body unit which has been fixedly mounted on the car. The electronic unit and the body unit is thus electrically connected to each other, thereby allowing the electronic unit to operate.
The body unit 1 is fixedly mounted on an automotive vehicle and as shown in FIG. 3, it has upper, lower and side walls defining a space for receiving the electronic unit 2. Two locking holes 1a, 1b (or 1c, 1d) are formed at the fore ends of each side plate for locking engagement with the associated locking projections provided in a tape deck or an electronic unit 2. When the tape deck 2 is operated, it is inserted into the space of the body unit 1 as indicated by an arrow to bring the locking projections into engagement with the locking holes formed in the body unit 1.
The term "electronic unit" used throughout the specification generally covers audio and video equipments, including, for example, radio receivers, such as AM/FM receivers, cassette decks, DAD players, such as CD (Compact Disk) players or TV or video sets. It should be noted, however, that the term "electronic unit" is not specifically limited to those mentioned above, but they are defined to mean electronic apparatus or equipments which achieve prescribed functions or operations when accommodated into the body unit and supplied with electric power.
In FIG. 1, there is shown a block diagram illustrating a conventional electronic unit of the type mentioned above.
In FIG. 1 a body unit 1 is installed in an automotive vehicle. The electronic unit 2 is detachably coupled to the body unit 1. The electronic unit 2 includes a connector 3, a CPU 4, and a timer 5. When the electronic unit 2 is coupled to the body unit 1, an enable signal or a coupled-status signal is supplied to the electronic unit 2 through the connector 3, whereas when the electronic unit 2 is decoupled from the body unit 1, a disable signal or a decoupled-status signal is supplied thereto through the connector 3. When the coupled-status signal is supplied to the terminal CH of the CPU 4 through the connector 3, the CPU 4 is placed in a start mode whereat clock pulses are issued from a terminal TG of the CPU 4 and a start signal is issued from a terminal IH thereof. When, on the other hand, the decoupled-status signal is supplied to the terminal CH of the CPU 4 from the connector 3, the CPU 4 is placed in a stop mode whereat the issuance of the clock pulses from the terminal TG is halted and a stop signal is issued from the terminal IH. The CPU 4 is reset in response to a reset signal supplied to its reset (R) terminal. The terminal IN of the timer 5 is supplied with the clock pulses from the CPU 4 and the reset signal for resetting the CPU 4 is issued from a terminal OUT of the timer 5 when the clock pulses are not received for more than a predetermined period of time. The reset signal is not outputted from the terminal OUT when the stop signal is received at the terminal CN.
Although not indicated in the figure, a large quantity capacitor or a secondary battery is provided in the electronic unit 2 for supplying electric power to both the CPU 4 and the timer 5 when the CPU 4 is placed in the stop mode.
Next, operation will be described.
When the electronic unit 2 is coupled to the body unit 1, the electronic unit 2 is powered by the body unit 1 and is allowed to perform prescribed operations responsive to the coupled-status signal supplied from the body unit 1 to the terminal CH through the connector 3. When the electronic unit 2 is decoupled from the body unit 1, the decoupled-status signal is supplied to the terminal CH of the CPU 4 and the CPU 4 in turn terminal IH to the terminal CN of the timer 5, whereupon the CPU 4 is placed in the stop mode. Hence, the clock pulses are no longer issued from the terminal TG. When the stop signal is supplied to the terminal CN of the timer 5, the latter stops its operation and is also placed in the stop mode. In the stop mode of the timer 5, the reset signal is not issued from the terminal OUT. Therefore, the CPU 4 which has been placed in the stop mode is never reset to the initial condition. In the stop mode, the CPU 4 holds the contents of a memory (not shown) with a little amount of power consumption.
The electronic unit 2 is provided with a release function to protect the electronic unit 2 from run-away condition of the CPU 4 occuring for some reasons. To this end, the timer 5 is designed to be reset whenever the timer 5 is supplied with clock pulses of a given period T from the terminal TG of the CPU 4. After elapse of a predetermined period of time t upon resetting the timer 5, the timer 5 outputs the reset signal from its terminal OUT. However, if the timer 5 is again reset by the subsequent clock pulse before expiration of the predetermined period of time t, the timer 5 does not output the reset signal to the CPU 4 so that if the relationship between the period T and the period of time t is set to T&lt;5, the timer 5 never outputs the reset signal during the normal generation of the clock pulses from the CPU 4.
If the runaway condition of the CPU 4 should occur for some reasons, the clock pulses may not be normally fed out from the CPU 4. Therefore, the timer 5 is not reset before expiration of the predetermined period of time t and thus the reset signal is outputted from the timer 5. The CPU 4 is in turn reset in response to the reset signal fed from the timer 5.
Since the prior art electronic unit is constructed as described above, there is a problem such that if an erroneous stop signal is fed from the CPU 4 due the CPU's runaway, the operation of the timer 4 is stopped in response to such an erroneous stop signal. Therefore, the CPU 4 cannot be reset notwithstanding the fact that the CPU 4 is in a runaway condition.